The present invention relates to lighting systems generally, and more particularly to an improved task light for providing substantially glare-free illumination within a task area. The improved task light of the invention is particularly adapted for use with office furniture systems having a task area bounded by at least a backwall and an overhead structure such as a shelf or binder bin under which the task light can be mounted. Other applications of the improved task light of the invention include any application in a large or small architectural environment having task areas that call for task lighting in addition to general ambient lighting.
A poorly lit task area leads to visual discomfort and fatigue that can greatly affect efficiency in completing visual tasks, such as reading and writing. The problem most associated with poor task lighting is reflected glare and veiling reflections, that is, glare that results when the source of the task light is reflected back into the field of view of a person working at the task area from a specular or semi-specular surface or object, such as a desk top, magazine page, or ordinary matte paper. (Reflected glare and veiling reflections will sometime hereinafter be referred to as simply "reflected glare".) Another source of glare is direct glare which occurs when a light source, which may have a surface brightness in the range of 3000 footlamberts as compared to much lower brightness levels on surrounding surfaces (in the range of 100 footlamberts), is within the field of view of the person working at a task. This situation particularly occurs with task lights mounted at a fixed height, such as an under-the-shelf task light. While normally out of view for a person whose eye level is above the task light, the intensely bright source of the task light will often be noticed by a person of short stature with a lower eye level.
Whether the glare is direct or reflected, the result is visual discomfort that is annoying, distracting, and often visually disabling.
Another factor that contributes to the visual comfort of task lighting is the distribution of the light within the task area. It is known that visual comfort in spaces where tasks are performed, such as the office environment, relate to the uniformity of lighting in the space. Office lighting systems, and particular indirect lighting systems, have been devised to increase the overall uniformity of ambient lighting and to decrease contrast brightness on wall surfaces and ceiling surfaces. A difficulty arises, however, when furniture elements, such as office systems furniture, are introduced into the room or architectural space. Such furniture elements typically include partition walls, overhead shelves, binder bins, and the like that creates shadowy areas on task surfaces and in and around the task area. These shadowy areas create visual discomfort, even if they do not cover a visual task. This is because darker shadowy areas contrast with the lighter surrounding areas making it more difficult for the eyes to comfortably adjust to the task lighting environment. Shadows also tend to give the person performing the task the sense of inadequate light. The response to this perceived inadequacy is often to increase the amount of task lighting within the task area. This approach is not only energy inefficient, but also exacerbates problems of reflected glare and veiling reflections.
Heretofore, various task lights have been designed that attempt to increase visual comfort and reduce glare. These prior approaches generally seek to shield the task light from direct viewing, or seek to reduce reflected glare by modifying light distribution patterns. For example, U.S. Pat. No. 5,115,380 issued May 19, 1992 to Huisingh discloses a fixture having a flat lens with a prismatic structure that refracts downwardly light emanating at high viewing angles from the front of the fixture that might otherwise be within the field of view of an adult of normal stature. However, Huisingh does not prevent direct glare at lower viewing angles that occur when eye level is closer to the level of the table top. Thus, the problem of direct glare is not necessarily avoided for people of short stature. Also, because the light source of Huisingh is positioned directly above the lens, the lens will exhibit a hot spot and will be a source of reflected glare. The asymmetry of the prismatic configuration of the Huisingh lens would further create a source of reflected glare by providing areas of contrast brightness across the lens. The only way to eliminate these sources of reflected glare in Huisingh is to reduce the light output of the fixture so that the brightness of the brightest part of the lens is reduced to the point where distracting surface reflections cease to occur. This solution, however, results in an unacceptable trade off: with the reduction in reflected glare, adequate illumination level at the task surface is lost.
Another approach to reducing reflected glare and veiling reflections from a task surface is disclosed in U.S. Pat. No. 4,432,044 issued Feb. 4, 1984, to Terry L. Lautzenheiser. The Lautzenheiser patent discloses a fluorescent task light having a rotatable masking sleeve surrounding the fluorescent lamp. The masking sleeve selectively masks the transmission of light emitted from portions of the lamp so as to reduce veiling reflections as seen from particular positions in front of the work surface. One disadvantage of such an approach is that while veiling reflections may be reduced at particular observation angles, they will not be reduced at others. Thus, if a person sitting in front of a desk or other task surface moves his or her visual task, such as a magazine page, or if the person himself or herself moves in relation to the visual task, then the veiling reflections may reappear requiring an adjustment of the fixture.
Lautzenheiser has other disadvantages. Because it masks only a portion of the lamp's surface, when the masking sleeve is adjusted for optimal control of reflected glare, it leaves exposed areas of lamp brightness that can be a source of direct glare. The exposed bright areas of the lamp are also detrimental to achieving uniform light distribution patterns, particularly on the back wall of a task area.
The present invention overcomes the disadvantages of prior task lights by providing an improved task light that eliminates the source of direct glare from any position in front of the task light, whether the observer's eye level is near the task surface or above the task light. The invention also reduces and can substantially eliminate the source of reflected glare within the task area regardless of the observation angle and without the need to adjust the fixture. The invention further provides for an improved task light and method that eliminates the discomfort associated with visual tasks undertaken in areas which are not uniformly lit and which have various and contrasting areas of brightness. The invention still further provides an improved task light that requires an overall reduced light output to create a comfortably lit task environment, and that is therefore energy efficient.